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the proposed waste bank. Cuts made for the railroad track alignment expose the Rollins <br />• Sandstone Member of the Mesa Verde Formation. This formation is described as "brown to <br />gray, fine- to medium-grained sandstone and grey shale; commercially important coal beds in <br />lower part; Rollins Sandstone Member at base" (USGS, 1976). Mining operations at the <br />Sanborn Creek Mine occur within the coal beds of the Mesa Verde Formation. The toe of the <br />proposed coal mine waste bank will be founded on the Rollins Sandstone Member of the Mesa <br />Verde Formation. Mapping of the Rollins Sandstone at these outcrops showed various degrees <br />of weathering, most of which occurs near the top of the outcrop. The weathered sandstone <br />breach easily with a hand pick along bedding planes. Below the highly weathered upper <br />sandstone is hard, competent sandstone that is very difficult to break with a pick. Within the <br />highly weathered sandstone, there is a seam of red clayey material that was very soft and <br />easy to break with a pick. This seam was an average thickness of 2 inches. <br />According to geologic maps for the area (USGS, 1978b-, rockfalls are the only hazard at this <br />site. This was evident in the vertical rock outcrops above the proposed coal mine waste bank, <br />and the colluvial material found on the hillside. Rockfalls are not expected to be a factor in <br />design, but may prove to be a maintenance issue, i.e., removing fallen rock fragments from <br />. the waste bank during the lifetime of the project. No remedial activities need to be conducted <br />to prevent rockfalls in the area. <br />2.2 SUBSURFACE CONDITIONS <br />Due to steep terrain and vehicle access problems, one geotechnical borehole was completed <br />at the end of the West Yard storage area. This location was optimal in that rig access was <br />available and the use of the railroad right-of way could be avoided. This borehole was drilled <br />to confirm depths of colluvium/alluvium; obtain material strengths; and confirm the continuity <br />of the Rollins Sandstone with the bedrock outcrops mapped near the toe of the proposed <br />waste bank as well as moderately deep groundwater conditions. The location of this borehole <br />is shown on Figure 2.1. <br />• <br />95256/1424.RPT Coel Mine Weete eenk Design for the Sanborn Creek Mine <br />October 1998 WESTEC, Ins. 3 <br />